Thin silicon dioxide (SiO.sub.2) films have a wide range of applications in the semiconductor industry. These films are typically formed by several methods, including thermal oxidation of silicon, plasma enhanced chemical vapor deposition (glow discharge) of silicon dioxide, plasma anodization, and plasma oxidation. While silicon dioxide formed by thermal oxidation is often of the highest quality, the temperatures required, i.e. about 1100.degree.-1200.degree. C., are too high for some applications.
There have been some efforts to reduce the process temperature for growing or depositing SiO.sub.2. For example, in U.S. Pat. No. 4,409,260, Pastor et al. disclose a chemical vapor deposition (CVD) method for growing a uniform oxide layer on a silicon substrate. Pastor et al. carry out their process at about 750.degree. C.
Plasma oxidation involves subjecting the substrate, such as silicon, to a glow discharge of oxygen to grow an oxide film. Plasma oxidation is disadvantageous for semiconductor applications in that the resulting silicon dioxide films, particularly the film interface, are frequently of poor quality. In addition, the growth rate is very slow and the thickness of the resulting film is extremely limited.
For example, in the report "Plasma Anodization of Metals and Semiconductors" in the Journal of Vacuum Science and Technology, Vol. 7, no. 2, p. 332, 1970 is described the process of growing an oxide on aluminum. This process produces films of only about 20 angstroms (.ANG.) in thickness using plasma oxidation without bias.
Two recent patents by Ray et al. describe refinements in plasma oxidation parameters. U.S. Pat. No. 4,323,589 discloses using pressures of 10 mTorr and up during plasma oxidation to improve oxide growth which is reported to occur at temperatures between 300.degree. and 550.degree. C. In U.S. Pat. No. 4,323,057 the temperature rather than pressure is controlled. While temperatures of 300.degree.-800.degree. C. are disclosed, only 500 .ANG. of SiO.sub.2 is grown on silicon in 3 hours at 650.degree. C. by this method. This provides a growth rate of only about 3 .ANG./minute. It is disclosed that this growth rate slows at substrate temperatures below 650.degree. C., with no work reported below 300.degree. C.
Besides the slow growth rates of the low temperature (300.degree.-500.degree. C.) oxidation methods, these methods are further limited in that the silicon dioxide films provided have poor physical and electrical properties as compared to thermally grown oxides. Specifically, most films produced by such prior art oxidation methods have a poor interface between the silicon and silicon dioxide and are usually lacking in density.
Further, many applications in the semiconductor industry require the growth of an oxide on a silicon film which overlies a substrate which is sensitive to temperatures above about 300.degree. C. Therefore, a method of growing a film of semiconductor quality silicon dioxide at temperatures below 300.degree. C. with a superior silicon/silicon dioxide interface and sufficient density has been sought.